No, I have not been searching the boaty forums for support. I was searching the internet for reviews of Steel Developments and only found Pikey Dave' s post.
I find some assurance with the fact that so many claim to have had exemplary service, however, I clearly have not.
I sent a propeller in to be repaired as a matter of urgency as I was disabled in Great Yarmouth. The chap came back to me saying he couldn't repair it which is fair enough I got a refund and asked for the propeller back as I needed it desperately as a template for a new one.
Unfortunately, to cut a long story short, I never got it back despite multiple requests for it.
So, to conclude, it's great to see so many happy customers but as the original post asked about them, then it's only valid that the negative experiences be known too.

Assuming it is all as you report I can't believe they "lost" your old prop... or kept it for devious means. Did you ask for a refund of it's value as a damaged bronze prop?

My last experience of SD was buying a non-gen cheaper new prop for a 15hp from them and finding (nit picking but a legit issue) it didn't meet the performance of the original. I'd used the new one for a week long holiday in Scotland and it was probably some weeks from the original purchase date I made a brief phone call to report the problem. They sent me a new OE Mercury prop at no extra charge for its much higher retail price or the extra postage.

As previously stated, I have visited the premises which is a residential property with a workshop in the rear garden. It looks like a husband & wife small business, so the claim that someone's on holiday is probably genuine. On previous experience of dealing with them, I'm sure that they would resolve the situation, given the opportunity.
As an aside, if you look at current scrap metal prices, I'm surprised they aren't charging to store the old prop, seeing as the 4rse has dropped out of the market.

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Rule#2: Never argue with an idiot. He'll drag you down to his level & then beat you with experience.
Rule#3: Tha' can't educate pork.
Rule#4: See rule#5